Abstract Spina bifida (SB) is the most common cause of lifelong childhood paralysis in the United States. SB results from the incomplete closure of the neural tube during the fourth week of gestation. The exposed spinal cord sustains intrauterine chemical and mechanical trauma, leaving children with lifelong paralysis, bowel and bladder incontinence, musculoskeletal deformities, and cognitive disabilities. These disabilities require extensive medical care and ongoing physical and cognitive rehabilitation, making SB one of the most costly childhood diseases. Recent studies ? including our own ? have suggested that fetal interventions with stem cells or other techniques have the potential to improve the prognosis of children born with this devastating disease. While the medical and scientific community has never been better positioned to develop new groundbreaking therapies for SB, the field suffers from a lack of suitable animal models. To accurately model SB, animals must have a long gestation, tolerate surgical manipulation of the fetus, and be sufficiently developed at birth to allow for the assessment of locomotor function. Commonly used animal models of SB include rats, rabbits, and sheep. To date, small animal models have been largely unsuitable for the development of new therapies; due to their small size and short gestation surgical manipulation of the fetus cannot be performed at an early enough gestational age to accurately model human SB. Furthermore, functional locomotor data cannot be collected from these models as neither rats nor rabbits are ambulatory at birth. While large animal models have longer gestational times, are more suited for fetal manipulation, and are ambulatory shortly after birth, they are prohibitively expensive and labor intensive. To statistically power a single arm of a sheep study will cost well over $100,000 and can take a team of surgeons and veterinarians an entire year to complete. We propose to develop a high-throughput, cost effective small animal model of SB using guinea pigs. Guinea pigs have a natural history that makes the species uniquely suited for SB in utero treatment research. Guinea pigs have the longest gestation of any commonly used small animal models, three times as long as rats and twice as long as rabbits. Additionally, guinea pigs represent the only commonly used small animal model capable of ambulation and independent feeding at birth. We propose to use guinea pigs to develop a reproducible small animal model of SB that will allow investigators to quickly and economically assess the effectiveness of new in utero therapies.